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Lunar Laser Rangin

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  • Feb. 2013
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Lunar Laser Ranging
I did my presentation in class on radar guns and the science behind them. With radar guns the most common but older technology uses radio waves and the principles of Doppler shifts to calculate the speed of an object. The newer, more precise technology is called LIDAR (Light Detection and Ranging) technology that uses laser pulses and the speed of the light to calculate speeds. To give a quick summary: the old radar guns measure the change in frequency of a radio wave bounced off a moving object while the LIDAR systems measure the change in time it takes two light pulses of lasers to hit a moving object and return. This laser technology is now being used to track the moon’s orbit, measure gravitational forces, and challenge Einstein’s theory of relativity. Lunar laser ranging is the process of “pinging” laser pulses off reflectors placed on the moon and measuring the time it takes for the lasers to return. Since we know the speed of light we can accurately measure the distance the light traveled. On average the time it takes for light to make the roundtrip is between 2.34 to 2.71 seconds depending on how far away the moon is at that moment. The distance ranges from 351,000 km to 406,000 km. This experiment is possible because in 1969 the Apollo 11 astronauts placed retroreflector arrays on the lunar surface. Following this first mission the Apollo 14 and 15 missions followed suit and placed corner cube retroreflector arrays on the lunar surface. The three Apollo reflectors in combination with a French built reflector left by the Soviets allow scientists to accurately map the moon as it orbits and rotates. These reflectors require no power and have been operating normally since they were installed nearly forty-three years ago. Scientists make measurements using each of the four available reflectors over the course of a half-hour period. This is repeated every few nights giving us a wealth of data to use in exploring the effects/behavior of...